In a carriage printer, such as an inkjet carriage printer, a printhead is mounted in a carriage that is moved back and forth across the region of printing. To print an image on a sheet of paper or other recording medium (sometimes generically referred to as paper herein), the recording medium is advanced a given distance along a recording medium advance direction and then stopped. While the recording medium is stopped and supported on a platen, the printhead carriage is moved in a direction that is substantially perpendicular to the recording medium advance direction as marks are controllably made by marking elements on the recording medium—for example by ejecting drops from an inkjet printhead. After the carriage has printed a swath of the image while traversing the recording medium, the recording medium is advanced, the carriage direction of motion is reversed, and the image is formed swath by swath.
In order to produce high quality images, it is helpful to provide information to the printer controller electronics regarding the printing side of the recording medium, which can include whether it is a glossy or matte-finish paper. It is well-known to provide identifying marks or indicia, such as a bar-code, on a non-printing side of the recording medium to distinguish different types of recording media. It is also well known to use a sensor in the printer to scan the indicia and thereby identify the recording medium and provide that information to the printer control electronics. U.S. Pat. No. 7,120,272, for example includes a sensor that makes sequential spatial measurements of a moving media that contains repeated indicia to determine a repeat frequency and repeat distance of the indicia. The repeat distance is then compared against known values to determine the type of media present.
For some applications, factors that can make it more difficult to reliably identify media type on the basis of sensed indicia include the random cutting position of the media, media slip during media advance in the printer, media advance motor control error, skew of the media, and the presence of a logo, indicating (for example) the manufacturer of the media. Incorrect identification of media type typically causes image quality degradation, because the printing conditions that are appropriate for the type of media that was mistakenly identified may be inappropriate for the actual type of media in the printer. What is needed, therefore, is a method having improved reliability for identifying media type on the basis of marks or indicia that have previously been provided on a surface of the recording medium.